Battery Health vs Usage Time

[ks-man]

Planning on buying a MBP soon...

I've read a bit around here about battery health. I was wondering how the health of the battery relates to the amount of time the battery will work for.

Is it simple arithmetic?
Max battery usage is 4 hours (just picking a number) so if your battery health is at 75% will it last for 3 hours and if at 50% it will last for two hours?

It seems that people get very concerned that their battery life dropped to 92-96% after 6-12 months, so that leads me to believe that the drop off in usage time may be more drastic. I would assume that after a year a battery lasting for over 90% of its initial full amount (in my example 92% of 4 hours would be 3 hours and 41 minutes) is still very good. This makes me wonder if a 90% battery health will only get you 50% of the original charge.

Also when do people typically buy a new battery? When battery health gets under 90%, 75%, 50%???

Thanks for the help. I'm just trying to get an idea of what I can expect when I get the MBP. I don't think it is unreasonable to have to spend $130 for a new battery after 18-24 months of use if I want to match the original full charge usage time. I'm wondering if people here start freaking out once their battery health goes under 98-100% despite the fact that it is a pretty minor deal in terms of how it will affect the real world performance.

Thanks again.

 

[Techguy172]

When the battery health drops it doesn't make much of a difference when it only drops 5-10% You may loose say 15-20 minutes off your battery. Now if it drops a lot then you will loose more Say it lost 50% then you will lose a little more than half your battery life.

I would buy a new battery at probably 75%. How long your battery lasts is all up top your usage patterns and how often you charge and discharge. So if you use it very little then it will last a long time if you use a lot it won't last as long. Although if you barely use it will die rapidly. It's just the way lithium batteries work.

Hope that helped!

 

[ks-man]

Hope that helped!

It did, thanks. While not an exact formula it does sound like a 10% loss in battery health will cost you 10% of usage time (far from a tragedy after 6-12 months).

Also when people say they've had 100 cycles, how is that measured? Is that anytime you unplug the laptop and then it recharges to full, or is that only for a full discharge and charge?

If you unplug your laptop every day and use it for 30 mins and then recharge it to full, after a year would you have 365 cycles?

Thanks.

 

[MarkMS]

It did, thanks. While not an exact formula it does sound like a 10% loss in battery health will cost you 10% of usage time (far from a tragedy after 6-12 months).

Also when people say they've had 100 cycles, how is that measured? Is that anytime you unplug the laptop and then it recharges to full, or is that only for a full discharge and charge?

If you unplug your laptop every day and use it for 30 mins and then recharge it to full, after a year would you have 365 cycles?

Thanks.

I was going to post in my own words, but I think this page from Apple will help you.

FROM APPLE.COM/BATTERIES

A charge cycle means using all of the battery’s power, but that doesn’t necessarily mean a single charge. For instance, you could listen to your iPod for a few hours one day, using half its power, and then recharge it fully. If you did the same thing the next day, it would count as one charge cycle, not two, so you may take several days to complete a cycle.